Self-holding unit having a reset delay circuit

ABSTRACT

A self-holding unit having a reset delay circuit is provided, which comprises a first capacitor charged by a reset signal that is applied when restoring or resetting self-held relay contacts. An RC time constant circuit including a second capacitor and a resistor is operative in response to the discharge of the first capacitor to activate a switching element, which operates to energize the reset coil upon lapse of a preset time interval determined by the RC time constant after the application of the reset signal, thereby achieving a time delay in resetting the relay contacts.

[ Nov. 26, 1974 SELF-HOLDING UNIT HAVING A RESET DELAY CIRCUIT Inventors: Takeshi Ukai, Tokyo; Kiyoshi Oshima, Yokohama, both of Japan Assignee: Ricoh Co. Limited, Tokyo, Japan Filed: May 22, 1973 Appl. No.: 362,873

Foreign Application Priority Data May 24, 1972 Japan r. 47-051470 US. Cl. 307/141 R, 317/142, 317/155.5 R int. Cl. H01h 47/18 Field of Search 317/155.5, 155.5 A, 137,

3,582,716 6/1971 Traina l. 317/l55.5

Primary Examiner-David Smith, Jr. Attorney, Agent, or Firm-Cooper, Dunham, Clark, Griffin & Moran ABSTRACT A self-holding unit having a reset delay circuit is provided, which comprises a first capacitor charged by a reset signal that is applied when restoring or resetting self-held relay contacts. An RC time constant circuit including a second capacitor and a resistor is operative in response to the discharge of the first capacitor to activate a switching element, which operates to energize the reset coil upon lapse of a preset time interval determined by the RC time constant after the application of the reset signal, thereby achieving a time delay in resetting the relay contacts.

3 Claims, 5 Drawing Figures PA EIIIE B 3.851.184

snmanrz FEED CUTTING EXPOSURE DEVELOP START I STOP DISCHARGE CHARGING CHARGING E I G. 5

SELF-HOLDING UNIT HAVING A RESET DELAY CIRCUIT BACKGROUND OF THE INVENTION The invention relates to self-holding unit having a reset delay circuit, and more particularly to such a unit in which the delay circuit becomes operative in response to a reset signal applied for releasing self-held relay contacts to reset the contact upon lapse of a'preset time interval.

A self-holding relay is known which comprises a relay coil that is energized upon application of an operating pulse to operate its associated contacts connected in a circuit to be controlled and subsequently maintains the contacts in their operative position by virtue of its residual magnetism, and a reset coil operative to release the relay contacts from their operative position upon application of a reset pulse. Such a relay is operable with a.c. pulses and now finds extensive applications. Where it is desired to provide a time delay in the resetting of such a relay, it is necessary to use a separate timer in combination therewith. By way of illustration, assume that such relay is used to control the energization of a charger charging a light-sensitive paper from a roll in an electrophotographic copying apparatus. The paper feed instruction can be utilized as an operating pulse for the relay, to close its contacts, whereupon the charger may be energized from a suitable supply to initiate the charging of the light-sensitive paper. Since the apparatus is constructed to interrupt the continuous supply from the roll by operation of a cutter when a given length of such paper has been supplied to the apparatus, it would appear that the instruction to operate the cutter may also be used as a reset pulse for the relay. However, this results in the inconvenience that the charger is rendered inoperative before the trailing end of the cut paper could pass under the charger. As a result, there occurs the need for a timer to pass the reset pulse to the relay only after a time delay so that the charger is deenergized at a preset time interval after the occurrence of the reset pulse.

' However, a conventional timer used for such purposes requires another power supply separate from that of the relay and involves a complicated interconnection with the relay, which adds to the cost.

SUMMARY OF THE INVENTION nal alone without requiring a separate power supply,

thereby greatly simplifying the construction as well as its connection with an external circuit. The unit includes a pair of capacitors which are connected in a manner to permit the residual charge thereon, upon resetting,to be utilized to energize the reset coil of the relay through a discharge circuit, thereby allowing an efficient use of power and a repeated operation with an accurate timing. The circuit arrangement is such that the relay remains in its held position in the event of interruption of a power supply that is used to produce an operating signal during the time interval between the occurrences of the operating and reset signals. Because of the first capacitor which serves as a power supply,

the delay circuit advantageously maintains its proper LII operation if the normal power supply fails during the operation ofthe delay circuit. The operating pulse may be either a.c. pulse or square pulse, thus making the unit useful in a variety of applications.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an embodiment of the electrical circuit of the self-holding unit according to the invention;

FIG. 2 is a timing diagram illustrating the holding period of the relay and the time delay;

FIG. 3 is a schematic view showing the general arrangement of an electrophotographic copying apparatus employing a roll of light-sensitive paper;

FIG. 4 is a flow chart showing the sequence of operations occuring in the apparatus of FIG. 3; and

FIG. 5 is a timing diagram illustrating the relationship between the holding time and time delay of the relay when the invention is applied to the apparatus shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. I, there is shown an embodiment of the self-holding circuit having a reset delay circuit according to the invention. The unit includes a first pair of terminals 1 and 2 across which delay contacts RI for controlling an external circuit are connected, and a second pair of terminals 3 and 4 across which an operating pulse Pl, shown in FIG. 2, is applied. Connected in series across the terminals 3 and 4 are resistor R1, diode D1 and the operating coil Rl of a relay which is shunted by a diode D3. When the operating pulse is applied across these terminals to energize the operating coil, its associated relay contacts R1 are closed. The diode D3 conducts a back e.m.f. The unit further includes a third pair of terminals 5 and 6 across which a reset pulse P2, shown in FIG. 2, is applied. A series circuit comprising resistor R2, diode D2, resistor R3, the reset coil R1, of the relay and switching element SCR is connected across the terminals 5 and 6. A capacitor C1, which provides a power supply for a delay circuit to be described later, is connected between the junction between the diode D2 and resistor R3 and the terminal 6, and is shunted by a discharge circuit therefor which comprises an RC time constant circuit formed by resistor R4, variable resistor VR and second capacitor C2. In the present example, the switcing element is constituted by a silicon controlled rectifier (SCR), which is adapted to be supplied with a firing gate voltage when the second capacitor C2 in the RC time constant circuit is charged to a predetermined constant voltage. At this end, a constant voltage element SO having a bidirectional voltage characteristic, commercially available under the trade name of BIAC, is connected between the gate of the SCR and the junction between the variable resistor VR and the second capacitor C2 so that it conducts when the voltage across the second capacitor C2 reaches a predetermined value, to apply a firing gate voltage to the SCR. The gate of the SCR is also connected with the tenninal 6 through a resistor R5, and a diode D5 is connected between the junction between the variable resistor VR and the sec across the reset coil. It is to be noted that the reset coil R1 is wound in the opposite direction to that of the operating coil R1,.

In operation, when it is desired to operate the unit, a.c. pulse P1 such as shown in FIG. 2 is applied across the terminals 3 and 4 as an operating signal. The pulse applied passes through the resistor R1, and is half-wave rectified by the diode D1 before being applied to the operating coil R1 to energize it. Upon energization of the coil Rl,, the associated relay contacts R1 are closed to complete the circuit across the terminals 1, 2, thereby allowing an external circuit connected thereto to be energized. As mentioned previously, once energized, the operating coil R1 is adapted to maintain its excited condition by virtue of the residual magnetism even after the operating pulse is removed, so that the relay contacts Rl remain in its operative or closed position, thys self-holding the relay. When resetting the unit, a.c., pulse P2 as shown in FIG.'2 is applied across the terminals 5 and 6. The pulse P2 passes through the resistor R2, and is half-wave rectified by the diode D2 to charge the capacitor C1. The charge on the capacitor Cl discharges through the path including the resis tor R4, variable resistor VR and second capacitor C2, thereby charging the latter capacitor C2; when the capacitor C2 is charged to a predetermined voltage in excess of the breakdown voltage of the constant voltage element SO, the latter conducts and applies a firing voltage to the gate G of the SCR, which therefore conducts. The residual charge on the first capacitor C1 now discharges through the resistor R3, and the residual charge on the second capacitor C2 also discharges through the diode D5 and the resistor R3, bothof such discharge currents flowing through the reset coil R1 of the relay. Because of the reverse winding of the reset coil R1 from the direction in which the operating coil R1 is wound, the described energization of the reset coil by the discharge current from the capacitors acts to eliminate or substantially reduce the residual magnetism produced as a result of the application of the operating pulse, thus releasing the self-holding of the relay contacts R1 Thus it will be seen that the relay contacts R1 will be opened after lapse of a time delay 1' (see FIG. 2) determined by the RC time constant circuit following the application of the reset pulse P2 to the terminals 5 and 6, and therefore that the holding period of the relay contacts Rl extends from the application of the operating signal P] unit to the energization of the reset coil RI 2 which is controlled by the RC time constant circuit, as depicted in FIG. 2. The length of time delay 1 is determined by the values of resistor R4, variable resistor VR and second capacitor C2 included in the RC time constant circuit; or 'r K (R4 VR)'C2, where K is a constant.

While in the embodiment described above, the switching element is shown as SCR and the constant voltage which is used to apply the firing voltage as BIAC, it should be understood that any other elements having equivalent functions can be substituted therefor.

As a further illustration, an exemplary application of the unit according to the invention to an electro'photographic copying apparatus is schematically shown in FIG. 3 as comprising a roll of light-sensitive paper 7, feed rollers 8a, 8b feeding the paper toward a charger 9, and a cutter 10 interposed between the rollers and the charger for cutting the paper when a given length thereof has been fed. The light-sensitive paper fed is charged by the charger before being passed to an exposure station 11 where the charged light-sensitive paper is exposed imagewise, followed by devolpment at 12 and discharge to the exterior of the apparatus. A copying apparatus of the type described is adapted to undergo a continuous process comprising the steps of Specifically, when an instruction for paper feeding issues, an operating pulse PI is derived therefrom to close the relay contacts R1 and energize the charger. Subsequently when the cutter 10 is actuated, a reset pulse P2 is derived from such operation of the cutter and is applied to the delay circuit which is arranged to have a delay interval 1- corresponding to the length of required for the trailing end ofthe cut light-sensitive paper to pass under the charger 9. Thus the charger 9 remains energized for a time period To (FIG. 5) which is equal to the sum of the time interval from the initiation of paper feeding to the actuation of the cutter l0 and the delay time interval 1-, thus allowing the light sensitive paper fed into the apparatus to be charged throughout its length or fromits leading end to its trailing end.

- What is claimed is:

l. A self-holding unit having a delay circuit comprising relay means operative upon application of an operation pulse for holding itself in its two setting positions selectively, a first capacitor adapted to be charged by a signal pulse, a resistor and a second capacitor connected in series with the first capacitor to form an RC time constant circuit, and switch means adapted to be rendered conductive when said second capacitor is charged to a predetermined voltage upon discharge said first capacitor for permitting application of the operation pulse from both said capacitors to said relay means for setting said relay means to one of its said po sitions.

2. A self-holding unit according to claim 1 in which the switching element is constituted by a silicon controlled rectifier which is adapted to be supplied with a firing gate voltage through a constant voltage element having a bidirectional voltage characteristic.

3. A self-holding unit according to claim 1 further including diode means adapted to permit discharge of said second capacitor therethrough upon the conductive condition of said switch means but normally not to 

1. A self-holding unit having a delay circuit comprising relay means operative upon application of an operation pulse for holding itself in its two setting positions selectively, a first capacitor adapted to be charged by a signal pulse, a resistor and a second capacitor connected in series with the first capacitor to form an RC time constant circuit, and switch means adapted to be rendered conductive when said second capacitor is charged to a predetermined voltage upon discharge said first capacitor for permitting application of the operation pulse from both said capacitors to said relay means for setting said relay means to one of its said positions.
 2. A self-holding unit according to claim 1 in which the switching element is constituted by a silicon controlled rectifier which is adapted to be supplied with a firing gate voltage through a constant voltage element having a bidirectional voltage characteristic.
 3. A self-holding unit according to claim 1 further including diode means adapted to permit discharge of said second capacitor therethrough upon the conductive condition of said switch means but normally not to permit charge of said second capacitor therethrough. 